2-Amino-5-chloropyridine was first prepared by Tschischibabin [Chem. Zentr. 99II, 1670 (1928)] by chlorinating 2-aminopyridine in alcoholic solution. English et al, [J. Am. Chem. Soc., 68, 453 (1946)] and Van Zweiten et al., [Rec. Trav. Chim. 80, 1072 (1961)] prepared 2-amino-5-chloropyridine in 54 percent yield in 20 percent aqueous sulfuric acid at 25.degree.C. Under such conditions significant amounts of 2-amino-3,5-dichloropyridine were produced as side products and low yields of the monochloro product were obtained.
2-Amino-5-chloropyridine also was prepared by reacting 2-aminopyridine with concentrated hydrochloric acid in the presence of an oxidizing agent. [Pharmazie, 19 (10), 677 (1964)]. Yields of the monochloro product of about 70 percent were obtained by this process with relatively slight formation of other chlorination products.
It was not recognized previously that selective mono-chlorination and higher yields of product are obtained by efficient protonation of the 2-aminopyridine reactant in a strongly acidic medium and chlorination of the selectively reactive protonated species.
Thus, it is an object of this invention to provide a process for preparing 2-amino-5-chloropyridine with only minimal concomitant production of the dichloro over-chlorination product.
It is a further object of this invention to provide a process for preparing 2-amino-5-chloropyridine in greater yield than previously has been accomplished.